The present invention relates to an apparatus and a method for acquiring and processing spectrographic information, particularly of moving media, and for the recognition, validation, and screening of such media. The invention has particular application in the field of self-service terminals (SSTs) and in recognition of banknotes and similar media, and detection of forgeries. In its broader aspects the invention has application in verifying or confirming the source or validity of other items or products.
A growing number of financial and similar transactions are carried out by means of self-service terminals (SSTs) such as automated teller machines (ATMs). Many transactions involve the deposit of media, such as banknotes, into the SST to pay for some service or product, or simply to credit the deposit to a user""s bank account. Therefore, such SSTs require a media recognition mechanism to recognize and determine the value of the deposited media, and to validate the media and detect forged or inappropriate media, such as forged banknotes or foreign currency. Screening of media to identify worn, dirty, or damaged media may also be desirable, so that such media may be separated from clean media and removed from circulation.
A number of systems currently exist for media recognition, validation and screening, but these are generally complex and expensive, requiring high-density images to be taken of the media, and may experience difficulties in handling media at the relatively high speeds necessary for real-time processing of banknotes within an SST, and so may extend the time taken to complete a transaction by an unacceptable degree.
Other systems are available that are low-cost, but these systems may only be used with a single type of currency or with a small set of currency types.
It is among the objects of embodiments of the present invention to obviate or alleviate these and other disadvantages of existing media validation systems. This may be achieved in part by making use of the optical properties of banknotes, in particular the complex color printing and patterns used on genuine banknotes.
According to a first aspect of the present invention, there is provided a method of validating selected properties of media, the method comprising the steps of:
a) providing a sensor apparatus comprising a monochromatic light source and a light detector, whereby the detector is positioned to receive only diffusely reflected light from the source;
b) locating an item of media in the path of the sensor apparatus;
c) activating the monochromatic light source, and detecting light diffusely reflected from the media, to provide an output from the detector containing data relating to the response of the media to said light source;
d) moving the media with respect to the sensor apparatus;
e) repeating step c) and optionally step d) at least once, so as to gather sample data from different areas of the media;
f) processing the sample data to determine a selected characteristic of the media; and
g) comparing the sample data against a reference database of data obtained from genuine media.
The above method may be utilized to rapidly and simply generate a data sample from the media characteristic of the media""s reflectivity at a single wavelength of light. xe2x80x9cLightxe2x80x9d in this context may mean any electromagnetic radiation, and not only visible light. For example, infra-red or ultraviolet light may be used. Similarly, any reference made herein to a particular xe2x80x9ccolorxe2x80x9d of light is to be understood as referring to light of a particular wavelength or band of wavelengths. Thus, a reference to xe2x80x9ccolored lightxe2x80x9d may refer for example to green light or to infra-red electromagnetic radiation.
Preferred embodiments of the invention may be used for recognition and validation of banknotes, for example, when such banknotes are entered into an ATM. For example, an ATM adapted to perform the method of the present invention may be provided with a light source and detector arranged as described herein, such that the path of a banknote entered into the ATM (the xe2x80x98test samplexe2x80x99) passes before the sensor apparatus. The light source is activated, and diffusely reflected light from the banknote is detected by the detector, which provides an output containing data relating to the response of the banknote to the light source.
The banknote is then moved a step further into the ATM, and a second sample taken of reflected light. This continues until several samples have been taken, yielding data characteristic of a stripe across the banknote.
The sample data is then compared in a xe2x80x98recognition searchxe2x80x99 against a reference database of data obtained from a range of denominations of banknotes; if the sample data matches data from a particular denomination of banknote, the test sample is identified as being of that denomination. Each denomination and source of banknotes will typically have a characteristic monochromatic sample profile across a particular stripe of the banknote.
Preferably, the media is moved linearly with respect to the sensor apparatus, such that the sample data is representative of a xe2x80x98stripexe2x80x99 across the media.
The method may further comprise the step of determining a linear dimension of the media. This enables the recognition search to be greatly simplified since a test sample need only be compared against reference samples of the same linear dimension, rather than all reference samples. That is, once a test sample has been rejected against a particular reference dataset as having different linear dimensions, there is no need to compare the actual data values of the two samples to reject the possibility of a match between the two samples. Preferably, the linear dimension of the media is determined according to the number of individual xe2x80x9cframesxe2x80x9d of data in the sample data, as this data is readily available from the sample data.
According to a second aspect of the present invention, there is provided a method of validating selected properties of media, the method comprising the steps of:
a) providing a sensor apparatus comprising a plurality of distinct monochromatic light sources and a light detector, whereby the detector is positioned to receive only diffusely reflected light from the sources;
b) locating an item of media in the path of the sensor apparatus;
c) activating a first monochromatic light source, and detecting light diffusely reflected from the media, to provide an output from the detector containing data relating to the response of the media to said light source;
d) moving the media with respect to the sensor apparatus;
e) activating another monochromatic light source, and detecting light diffusely reflected from the media, to provide an output from the detector containing data relating to the response of the media to said light source;
f) repeating steps d) and e) at least until each distinct monochromatic light source has been activated;
g) processing the sample data to determine a selected characteristic of the media; and
h) comparing the sample data against a reference database of data obtained from genuine media.
This aspect of the present method generates sample data comprising information from a plurality of wavelengths of light (for example, red, green and blue). This extra data may be used for more rigorous analysis of the sample than that provided by data obtained from light of a single wavelength.
In a variant of the invention, additional light source activation steps may be included prior to movement of the media; for example, data from each wavelength of light may be taken at a single xe2x80x98spotxe2x80x99 on the media, the media may be moved, and a further set of data readings taken at a second xe2x80x98spotxe2x80x99.
Preferably each distinct monochromatic light source is activated in a predetermined sequence. This ensures that the sample data is consistent across different samples, and may be readily compared.
In a preferred embodiment of the present invention, media identification and validation may be performed as separate steps. The initial identification of the media may make use of the data relating to the response of the media to a single wavelength of light only, for identifying the type of media (for example, denomination of banknote). Subsequent validation of the media may however comprise the additional step of comparison of data relating to the response of the media to a plurality of wavelengths of light against a reference database of data obtained from genuine media. Since the database size, and hence the time required to perform a comparison, will be greater for multi-channel data than single channel data, the initial identification of the type of media under scrutiny may be used to restrict the reference database to be searched to, for example, a specific denomination of banknote, prior to validation of the media with reference to multi-channel data. This technique is further preferred as media identification need be less rigorous than media validation, since a higher proportion of false positives or negatives may be tolerable at the identification stage than the validation stage.
The comparison of sample data and reference data may take the form of comparison of measured light levels for each wavelength of light directly, without further processing of the data; alternatively, or in addition, differences between measured light levels for pairs of wavelengths of light may be compared. For example, the difference between red and infra-red responses may be compared for the test and reference samples. Such a comparison may prove to be more resistant to variations between the same type of banknotes, and so provide a more robust method. Numerous other data comparison techniques may be used, as will be apparent to those of skill in the art.
In one embodiment, the comparison of sample data against reference data makes use of a Bayesian classifier algorithm, although any other robust pattern matching technique may be used. This technique is preferred when the data comparison is for purposes of identification of media only.
Alternatively, or in addition, the comparison of sample data against reference data makes use of a spatially dependent discrimination algorithm, giving greater weighting to some areas of the media than others. This embodiment is particularly preferred when validation of media is being conducted. This is to take account of the fact that certain parts of many media, particularly banknotes (for example, the Treasury Seal on US Dollar bills) are significantly more difficult to forge than other parts of the notes.
Preferably, the method further comprises the additional steps of:
normalizing the sample data with respect to the reference data for the same type of media; and
determining the condition of the media by reference to the degree of normalization required.
As a broad generalization, the degree of normalization required is proportional to the amount of degradation of the media. A layer of dirt on the media approximates a neutral density filter, which attenuates but does not distort the color information. These additional steps enable the method of the present invention to validate and identify dirty, worn or damaged banknotes with greater reliability than if no normalization is used. Further, the method may also be used to determine the degree of degradation of a banknote (by determination of the degree of normalization required), and so, for example, separate badly damaged notes from other notes, for removal from circulation.
According to a third aspect of the present invention there is provided an apparatus for sensing selected properties of media, the apparatus comprising a monochromatic light source, a light detector, and means for location of media in the path of the detector, whereby the detector is positioned so as to receive only diffusely reflected light from media located in the path of the detector.
It is desirable that the detector not receive light directly reflected from the media or transmitted directly from the light source to the detector, as such light does not contain any spectral information regarding the media to be detected. That is, such light corresponds solely to the emitted light, whereas diffusely reflected light contains information dependent on properties of the reflecting body.
Preferably, the source and detector are located within a holder. Conveniently, the source and detector are located within a plastic holder; although numerous other suitable materials will be apparent to those of skill in the art. It is preferred that the holder is of a light-absorbing material, to reduce possible problems arising from reflection of the light source. Conveniently also the holder is in the form of a planar disc.
Preferably, the light source and light detector are directed towards the same side of a plane. Preferably also the direction in which the light is emitted by the light source is at an acute angle with respect to the direction in which the light detector is directed. The preferred angle between the light source and detector is dependent on the spacing of the source and detector relative to the media; the preferred embodiment of the present invention has a vertical spacing of 9 mm between the detector and the media, and an angle of 60xc2x0 between the light source and detector.
Preferably, a plurality of distinct monochromatic light sources are provided. Conveniently, four distinct monochromatic light sources are provided. In a preferred embodiment of the invention, separate red, green, blue and infra-red light sources are provided. Preferably the light sources are arranged around the detector. Preferably the detector is equidistant from each of the light sources, at a central location. Conveniently also, each monochromatic light source comprises paired monochromatic light sources; most preferably, the members of each pair are diametrically opposed.
Preferably, each light source is a light emitting diode (LED).
Preferably, the light detector is a photodiode.
According to a fourth aspect of the present invention, there is provided a system for sensing selected properties of media, the system comprising a monochromatic light source, a light detector, and means for location of media in the path of the detector, whereby the detector is positioned so as to receive only diffusely reflected light from media located in the path of the detector, means for generating a timing signal, means for activating each light source in synchrony with the timing signal, means for recording signals from the light detector, and means for processing the recorded signals.
In a preferred embodiment of the invention, the system comprises a plurality of distinct monochromatic light sources, and the means for activating the light sources comprises means for activating each distinct monochromatic light source in turn in a specified sequence.
Preferably, the system further comprises means for moving an item of media with respect to the detector. Conveniently this means may comprise one or more rollers for moving the media. Alternatively, conveyors, slides or the like may be used. Preferably also, the system further comprises means for detecting the edges of the item of media. Preferably, the system still further comprises means for commencing and ceasing recording of signals on detection of the edges of the item of media. Conveniently, the edge detection means comprises one or more photosensors disposed in the path of the item of media; alternatively, means such as physical edge detectors, electrical resistance sensors, or the like may be used.
Preferably also, the means for moving an item of media comprises means for generating a signal after the moving means has moved through a predetermined distance. For example, where the moving means comprises a roller, the roller may generate a signal on each revolution. Preferably also, the signal is communicated to the timing means; more preferably the timing means includes a phase locked loop (PLL) circuit. This ensures that each sample reading is taken at regularly spaced intervals, regardless of system speed or variations in transport speed, so compensating for irregular movement of the media, and ensuring that the data collected from each test sample is consistent across different media. The phase lock loop ensures that timing signals to activate each light source are generated at intervals corresponding to movement of the moving means through a predetermined distance; and is preferably used in combination with a conventional timing device such as a clock circuit, which controls activation of each light source for a fixed time interval.
Preferably, the system further comprises means for orienting an item of media to a particular orientation with respect to the sensing apparatus. This may conveniently be an arrangement of guides, preventing insertion of media into the system in an incorrect orientation. Alternatively, or in addition, the orientation means may comprise an arrangement of guides for holding and turning a media item into a preferred orientation.
In one embodiment of the invention, the system may comprise two detectors, disposed so as to give readings from opposed faces of an item of media. This ensures that a large amount of available data may be collected on a single pass of the media.
According to a fifth aspect of the present invention, there is provided a self-service terminal (SST), comprising a system for sensing selected properties of media, the system comprising a monochromatic light source, a light detector, and means for location of media in the path of the detector, whereby the detector is positioned so as to receive only diffusely reflected light from media located in the path of the detector, means for generating a timing signal, means for activating each light source in synchrony with the timing signal, means for recording signals from the light detector, and means for processing the recorded signals.